Continuously variable voltage low impedance transformer assembly



Aug. 23, 1966 w. w. GIBSON ETAL 3,268,842 CONTINUOUSLY VARIABLE VOLTAGE LOW IMPEDANCE TRANSFORMER AS SEMBLY Filed Oct. 5, 1964 2 Sheets-Sheet l INVENTORS W/LL/AM H4 GIBSON 8414M? TILSE THE/l? ATTORNEYS Aug. 23, 1966 w. w. GIBSON ETAL 3,268,842 CONTINUOUSLY VARIA BLE VOLTAGE LOW IMPEDANCE TRANSFORMER ASSEMBLY Filed Oct. 5, 1964 2 Sheets-Sheet 2 INVENTORS WILL/4M H. GIBSON QIA/VS T/LSE flaw 7 6m THE/R ATTORNEYS United States Patent 3,268,842 CONTINUOUSLY VARHABLE VOLTAGE LOW HMPEDANQE TRANSFORMER ASSEMBLY William W. Gibson, Alameda, and Hans Tilse, Oakland,

Calif, assignors to Glenn Pacific Corporation, a corporation of California Filed Oct. 5, 1964, Ser. No. 401,532 6 Claims. (Cl. 336-147) Our invention relates to transformers and more particularly to a continuously variable low impedance transformer assembly.

Since any electrical apparatus operates most effectively at rated voltage, it is important that the rated voltage be supplied to such apparatus, and :be maintained as nearly constant as is possible from no load to full load. Where such loads are supplied through transformers, this means that the transformer must have good regulation.

One of the factors which adversely affects voltage regulation in a transformer is magnetic leakage. If there were no magnetic leakage, the ratio between the primary and secondary terminal voltages would differ from the turns ratio only by the relative small resistance drop in the windings. However, magnetic leakage contributes an additional component to the voltage drop through the transformer, in the form of a leakage reactance drop, and increases the departure of the voltage ratio from the ideal. Since this component of voltage drop is inductive, it not only increases with load, but also with frequency, and introduces a number of problems concerning regulation.

Leakage reactance is solely a function of the physical design of the transformer. It can be shown that the percent reactance drop varies directly with the number of turns, the thickness of the coils, the spaces between the windings, the average main length of turn, and inversely with the length of coils.

Some reduction can be made in the leakage reactance drop by interleaving sections of the secondary winding with sections of the primary winding so as to increase the close coupling between the two windings. This is a practical approach to such problem, but unfortunately, does not lend itself to transformers from which a continuously variable secondary voltage is desired.

Among the objects of our invention are:

(1) To provide a novel and improved transformer assembly having good voltage regulation from no load to full load, yet offering a continuously variable voltage range in the output circuit thereof;

(2) To provide a novel and improved transformer assembly of compact construction which will provide an output range of voltages which will remain substantially constant from no load to full load;

(3) To provide a novel and improved transformer assembly which will provide a continuous range of output voltages at high efiiciency in the operation of such assembly.

Additional objects of our invention will be brought out in the following description of a preferred embodiment of the same, taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a three-dimensional view of a transformer assembly embodying the present invention;

FIGURE 2 is a three-dimensional view of the transformer assembly of FIGURE 1, broken apart, to illustrate certain aspects of the invention.

Referring to the drawings for details of our invention in its preferred form, we have depicted the same as applied to three phase operation. A fixed transformer 1 is designed to have good regulation, and accordingly, the primary and secondary winding of each phase may be sectionalized and interleaved, and/or other precautions may be taken to minimize magnetic leakage to assure good regulation.

Electrical connections, preferably in the form of taps 3, are taken off the secondary winding of each phase at electrically spaced voltage points, which are preferably equally spaced electrically.

Adjacently disposed on a common base 7, is an output winding assembly involving three similar windings 11, each associated with a different one of the secondary windings of the three phase transformer 1. Such windings are mounted on a three-legged core 15 of iron laminations, the laminations being held together by clamping bolts 19 through angle strips 21 along the upper and lower ends'of the core which function also to provide lateral mounting flanges, which may be utilized for the mounting of the windings to the base 7 or for assembling of components in association therewith.

Each leg of the core is of rectangular cross section and supports one of the windings, the outer layer of each winding presenting at least one planar side. On such side the insulation is removed along a path 25 extending substantially the full length of the winding to expose or bare the adjacent turns in this outer layer.

For effecting an adjustable electrical connection to such windings, we provide a gang brush holder 31 for longitudinal movement along the exposed portions of the windings, such gang brush holder involving parallel spaced bars 33, 35 spanning the three windings and threadedly mounted on a pair of vertical screws 37, 39 rotatably supported adjacent the windings, with their ends journalled in suitable end plates 43, 45, one adjacent the lower ends of the windings and the other affixed to a mounting platform 47 at the upper end of the core.

These parallel bars carry brush holders 51, one opposite each of the conductive paths 25 provided along each of the windings. Each brush holder carries a set of brushes extending toward the proximate winding between the parallel bars and held in pressure contact with the conductive path on such winding by a tail spring. A terminal connection may be taken off from each brush holder, while a fixed terminal connection may be provided for each winding at one end thereof, preferably the lower end, of the embodiment illustrated.

The details of the brush holder are not of major significance to the present invention, such a brush holder being disclosed in the copending application of William W. Gibson for Welding Systems and Associated Adjustable Welding Reactor, S.N. 763,989, filed September 29, 1958, now Patent No. 3,212,040 of October 12, 1965.

One of the screws 37 may extend through its upper mounting plate and to the end of the screw thus exposed, is affixed a sprocket for chain drive connection 57 to a drive sprocket 58 on the shaft of a suitable drive motor 59, bracket mounted on the platform 47.

By coupling the driven screw 37 to the remaining screw 39 through a suitable sprocket chain coupling 61, both screws may be caused to rotate in unison, whereby simultaneous adjustment of the brush holders in either the up or down direction, along the exposed conductive paths 25 on the respective windings 11 may be effected.

Electrical connections from the electrically spaced taps 3 of each of the secondary windings of the transformer 1 are made to corresponding physically spaced points on one of windings 11, for which purpose, the windings 11 are each provided with appropriate t-aps 67. Since the transformer 1 has been designed to give good regulation, from no load to full load, the voltages derived therefrom and applied to the windings 11, will thus be stabilized from one contact to the other. Consequently, any leakage existing in the output windings 11 above the prevailing position of contact of the brushes will have ine3 significant, if any, influence on the output voltage determined by such position of the brushes.

From the foregoing, it will be apparent that the specific details of construction of the transformer 1 or the output winding assembly 9 are not fundamental to the present invention. What is important is the fact that applicants are essentially duplicating along the conductive paths of the output windings 11, the voltage conditions prevailing within the secondary windings of the transformer 1, and making such prevailing conditions available for obtaining a continuously variable output range of voltage.

The output windings 11, it will be recognized, thus function as auto-transformers in making available voltages derived from those impressed thereon from the transformer 1.

The transformer 1 need not be one having independent or isolated primary and secondary windings, as previously assumed, but may be of the auto-transformer type, one which has been designed to provide good regulation from no load to full load. When so designed, however, a continuously variable output voltage cannot be derived from such auto-transformer. The present invention makes it possible to maintain such good regulation while at the same time providing a continuously variable output voltage.

When the transformer 1 is of the auto-transformer type, voltage taps 3 will be taken off at suitable voltage points, preferably at equally spaced voltage points along the secondary winding as previously described, and electrically connected to the corresponding physically spaced points on the output windings 11.

When the taps 3 are at equal voltage spacings, and the taps 67 are at corresponding equal physical spacings, such spacings will assure uniform voltage per turn along the windings 11.

In the event it is desired that the output windings 11, provide a range of output voltages exceeding the maximum voltage derived from the transformer 1, the connections from the transformer 1 will be confined to less than the full length of the output windings and provision will be made for running the brushes beyond the highest voltage connection from said transformer.

It will be appreciated that the transformer 1, in designing the same for good voltage regulation, might have a voltage per turn ratio of the order of 4 to 20 volts per turn, while a much lower ratio or voltage per turn might otherwise be desirable. The present invention places no limit on the number of turns in the output windings, and accordingly such output windings not only will carry over the good regulation characteristics of the transformer 1, but will permit of a voltage per turn ratio of low value of the order of one volt per turn or less, if such ratio be desired.

From the foregoing description of our invention, it will be apparent that the same fulfills the objects thereof, and while we have illustrated and described the same in its preferred form, the invention is subject to alteration and modification without departing from the underlying principles involved, and we accordingly do not desire to be limited in our protection to the specific details illustrated and described except as may be necessitated by the the appended claims.

We claim:

1. A continuously variable low impedance transformer assembly comprising in combination,

a transformer having means providing low leakage reactance from no load to full load, to provide good voltage regulation,

a separate winding,

electrical connections from electrically spaced voltage points on the secondary winding of said transformer to corresponding physically spaced points along said separate winding to form parallel connections between said secondary winding and said separate winding, and means for obtaining a continuously variable voltage from said separate winding.

2. A continuously variable low impedance transformer assembly comprising in combination,

a transformer having means providing low leakage reactance from no load to full load, to provide good voltage regulation,

a separate Winding independent of said transformer,

electrical connections from equal electrically spaced voltage points on the secondary winding of said transformer to corresponding equal physically spaced points along said independent winding to form parallel connections between said secondary winding and said separate winding,

and means for obtaining a continuously variable voltage from said separate independent winding.

3. A continuously variable low impedance transformer assembly comprising in combination,

a transformer having means providing low leakage reactance from no load to full load, to provide good voltage regulation,

a separate winding,

electrical connections from electrically spaced voltage points on the secondary Winding of said transformer to corresponding physically spaced points along said separate winding to form parallel connections between said secondary winding and said separate winding,

and means for obtaining a continuously variable voltage from said separate winding, said means including an output terminal electrically connecting to a point on said winding, an exposed path of adjacent turns along said winding, and a slidable terminal in electrical contact with turns of said winding thus exposed.

4. A continuously variable low impedance transformer assembly comprising in combination,

a transformer having means providing low leakage reactance from no load to full load, to provide good voltage regulation,

a separate winding independent of said transformer,

electrical connections from equal electrically spaced voltage points on the secondary winding of said transformer to corresponding physically spaced points along said independent winding to form parallel connections between said secondary Winding and said separate winding,

and means for obtaining a continuously variable voltage from said separate independent Winding, said means including an output terminal electrically con necting to a point on said winding, an exposed path of adjacent turns along said winding, and a slidable terminal in electrical contact with turns of said winding thus exposed.

5. A continuously variable loW impedance transformer assembly in accordance with claim 1, characterized by said separate winding being on a core apart from said transformer.

6. A continuously variable low impedance transformer assembly in accordance with claim 4, characterized by said separate winding being on a core apart from said transformer, and said slidable terminal being a component part of a brush assembly mounted for slidable movement over said exposed path.

References Cited by the Examiner UNITED STATES PATENTS 925,102 6/1909 Hobart et al. 336148 X 1,422,653 7/1922 Berry 323--43.5 2,688,117 8/1954 Knopp 336- X 3,212,040 10/1965 Gibson 336149 LEWIS H. MYERS, Primary Examiner.

ROBERT K. SCHAEFER, Examiner. D. I. BADER, Assistant Examiner. 

1. A CONTINUOUSLY VARIABLE LOW IMPEDANCE TRANSFORMER ASSEMBLY COMPRISING IN COMBINATION, TRANSFORMER HAVING MEANS PROVIDING LOW LEAKAGE REACTANCE FROM NO LOAD TO FULL LOAD, TO PROVIDE GOOD VOLTAGE REGULATION, A SEPARATE WINDING, ELECTRICAL CONNECTIONS FROM ELECTRICALLY SPACED VOLTAGE POINTS ON THE SECONDARY WINDING OF SAID TRANSFORMER TO CORRESPONDING PHYSICALLY SPACED POINTS ALONG SAID SEPARATE WINDING TO FORM PARALLEL CONNECTIONS BETWEEN SAID SECONDARY WINDING AND SAID SEPARATE WINDING, AND MEANS FOR OBTAINING A CONTINUOUSLY VARIABLE VOLTAGE FROM SAID SEPARATE WINDING 